Many mass storage systems comprise housings that contain multiple removable modules that, in turn, contain storage media. For example, a rack enclosure may comprise a plurality of housings arranged in a vertically-stacked orientation with each housing comprising a plurality of drive cages, each cage being adapted to receive one or more removable drive modules that comprise multiple hard disks.
In designing a mass storage system, such as that described above, a significant amount of attention must be devoted to the design of the removable modules. For example, the configuration and dimensions of the removable module (i.e., “form factor”) are important in achieving high storage density. In addition, an insertion and removal mechanism typically is provided for the modules that enables a user to easily insert the modules into and remove the modules out from their cage. Furthermore, it may in some cases, be desirable to provide a mechanism for preventing modules of a certain type from being inserted into given bays of a cage that are adapted to receive modules of a different type.